Nature of transient inhibition of deoxyribonucleic acid synthesis in HeLa cells by parainfluenza virus 1 (Sendai)

Permeabilization of transformed mouse fibroblasts by 3'-O-(4-benzoyl)benzoyl adenosine 5'-triphosphate and the desensitization of the process

A photoreactive analogue of ATP, 3'-O-(4-benzoyl)benzoyl adenosine 5'-triphosphate (BzATP) altered the plasma membrane permeability of transformed 3T6 mouse fibroblasts to normally impermeant molecules as previously reported for ATP, but at lower concentrations. BzATP-induced permeabilization was modulated by pH, temperature, and the ionic composition of the medium similar to the permeabilizing effects of ATP. Conditions known to enhance ATP-induced permeabilization, such as treatment with the mitochondrial uncoupler carbonyl cyanide-m-chlorophenylhydrazone (CCCP) or the Ca2+-calmodulin antagonist trifluoperazine also enhanced BzATP-induced permeabilization. Conditions inhibitory to ATP-induced permeabilization, including chloride replacement or treatment with furosemide or dithiothreitol (DTT), inhibited permeabilization induced by BzATP. The ionic strength of the medium modulated the responsiveness of the cells to ATP and BzATP; a decrease in the ionic strength below isotonicity increased the sensitivity of the cells to the nucleotides, whereas an increase in ionic strength above isotonicity inhibited permeabilization. Prolonged exposure to ATP under non-permeabilizing conditions caused the cells to become insensitive to ATP and BzATP. The densensitization phenomenon provides support for the theory that the permeabilization process is mediated by a receptor for ATP.

Sensitivity of Burkitt lymphoma Daudi cells to inactive influenza virus

Interaction of UV-inactivated influenza A/X47 virus at high multiplicity caused a rapid inhibition in cellular protein and DNA synthesis, thus arresting Burkitt-lymphoma-derived Daudi cell multiplication, and eventually killing the cells. The mechanism of the cytolytic effect is presumably, linked to the increase in cell membrane permeability indicated by elevation in 51Cr release. This might be the consequence of the mass adsorption and/or penetration of viral particles.

A comparative study of permeabilization induced by extracellular ATP and by Sendai virus

Both Sendai virus and extracellular ATP induce membrane changes in 3T6 cells which allow passage of phosphorylated metabolites and normally impermeant aqueous solutes. The two processes share many features in common, including their kinetics and the effects of temperature, Ca2+, and various metabolic inhibitors. Furthermore, in each case permeabilization is preceded by net changes in intracellular cations. However, there are significant differences in that only ATP-dependent permeabilization is influenced by changes in the ionic strength of the medium, by inhibition of the Na+, K+, Cl- cotransporter and by preincubation of 3T6 cells with dithiothreitol.

Fusion of human erythrocytes induced by uranyl acetate and rare earth metals

Incubation of human erythrocytes with either uranyl ions (UO22+) or rare earth metals (La3+, Nd3+, Sm3+, Eu3+, Tb3+, Dy3+ and Yb3+) at 37 degrees C for 30-45 min resulted in the fusion of erythrocytes. Redistribution of membrane-associated particles was observed using colloidal-iron charge labelling and freeze-fracture electron microscopy. The fusion of erythrocytes induced by these agents, unlike Ca2+, did not exhibit the absolute requirement for phosphate. Moreover, agglutination and fusion by these agents was observed in neuraminidase-treated erythrocytes in contrast to Ca2+- and phosphate-induced fusion. Inhibitors of intrinsic transglutaminase activity partially inhibited (35-45%) the fusion induced by UO22+ suggesting that cross-linking of membrane proteins results in protein-free areas of lipid where fusion may be initiated.

Nature of permeability changes in membrane of HeLa cells adsorbing Sendai virus

Adsorption of Sendai virus to HeLa cells induced in them an increased permeability to K+, Na+, Ca++, deoxyglucose, but not to fluorescein. The stimulation of uptake of 42K was temperature-dependent, did not occur below 15 degrees C, and was not inhibited by ouabain. The virus-induced increase in the uptake and release of 42K and of 3H deoxyglucose could not be mimicked by treatment of cells with linoleic acid, a procedure which increased the fluidity of the cellular membranes. The stimulatory effect of 0.5 mM ATP on the release of deoxyglucose was enhanced several fold in the presence of Sendai virus. These results seem to indicate the possible involvement of membranal enzymes such as e.g. protein kinase in the permeability changes induced by Sendai virus.

Fluorescence polarization of DPH-labeled cells adsorbing viruses and its diagnostic potential

Mammalian or avian cells were labeled with a fluorescent probe DPH (1,6-diphenyl-1,3,5-hexatriene). Within a few minutes after adsorption of various naked and enveloped viruses, the degree of fluorescence polarization (P) of the DPH embedded in the adsorbing cells as measured at 37 degrees C, was reduced, a finding indicating a decrease in the microviscosity of the lipids in the cell membrane. This change of fluidity was proportional to the concentration of the adsorbing virus and could be abolished or inhibited by homologous specific antiviral sera, but not by heterologous sera. Potential use of fluorescence polarization tests is described for titration of virus concentration, as well as for serological identification of a virus.

Kinetics of drug transport and concurrent metabolism in human cell cultures I: theory

A method for evaluating the passive permeability and single-step metabolism of drugs in suspension cultures of mammalian cells was formulated assuming linear kinetics. It was assumed that the metabolizing enzymes are driven by endogenous substrates present in steady-state quantities. The presence of the drug in radiolabeled tracer quantities was assumed to cause only a small perturbation from the endogenous steady-state operating point. The time course solutions for the drug and its metabolite are given in terms of macroscopic constants, and their physical interpretations are given in terms of metabolic and transport parameters.

Early changes in the membrane of HeLa cells adsorbing Sendai virus under conditions of fusion

Adsorption of Sendai virus at high multiplicity (500-1,000 HAU/10(6) cells) to HeLa cells grown in monolayers causes immediate changes in the ion barrier of the cell membrane, as well as changes in the morphology of the virus-treated cells. Within minutes of adsorption the cells begin to lose potassium and an extensive influx of ions into the cells occurs. Concomitantly with these changes, the cell membrane becomes depolarized, and the resting potential across its membrane decreases. Twenty to sixty minutes post adsorption the damage to the cell membrane is repaired, and both the potassium uptake and the resting potential return to their pre-exposure values. Scanning electron-micrographs of Sendai infected cells incubated at 37 degrees C show formation of bridging microvilli in a zipper-like fashion within two to five minutes post-adsorption; 30 to 60 minutes thereafter the majority of cells in the monolayer are fused. Biochemical changes induced by virus adsorption and the role of Ca++ ions in the observed effects are discussed.

Picorna- and togavirus infection of cells detected by gas chromatography

Viral infection of cells causes chemical and metabolic changes, which can be detected by gas chromatography (GC) of ether extracts of supernatant fluids and cell homogenates before any significant damage to the cells is observable microscopically. The characteristic and specific GC patterns obtained from BHK-21 and Vero cell cultures infected with encephalomyocarditis, polio, echoviruses, and a togavirus make it possible to distinguish between these infecting viruses. The appearance of 1 or 2 compounds, represented by GC peaks with TR values of 302 and 677 seconds seems to be specific for these viruses. Other peaks found in the supernatant media 1-2 hours after infection probably represent cell constituents leaking into the medium as a result of damage to the cell membrane by the invading virus.

Thymidine metabolism and DNA synthesis in Newcastle disease virus-infected cells

The inhibition of thymidine incorporation into DNA in Newcastle disease virus-infected cells has been studied. At 6 h after infection of L-929 cells at high multiplicity, transport of exogenous thymidine across the cell membrane was inhibited. The kinetics of this inhibition, decreased Vmax with no change in Km, suggest that there are fewer sites available for transport in infected cells. The conversion of thymidine to dTTP was not inhibited. Equilibrium of exogenous thymidine with the acid-soluble pool occurred more slowly and at a lower level of radioactivity than in uninfected cells, and there was a reduction in the rate of incorporation of exogenous thymidine into DNA. The reduction of incorporation into the pool and into DNA was proportionate. The size of total cellular dTTP pools was changed very little in infected cells. DNA synthesized in infected cells in the presence of [3H]BrdUrd had reduced incorporation of tritium but similar buoyant density to that from uninfected cells. The results show that Newcastle disease virus inhibits DNA synthesis directly and, in addition, decreases thymidine transport. Together these account for the overall decrease in thymidine incorporation into DNA of infected cells.

Transient inhibition of polyoma virus synthesis by sendai virus (parainfluenza I). II. Mechanism of the interference by inactivated virus

The mechanism of the transient inhibition of polyoma virus synthesis by betapropiolactone-inactivated Sendai virus was studied. Polyoma virus early functions did not appear to be affected, although deoxyribonucleic acid (DNA) and structural protein synthesis were inhibited 60 and 35% respectively. The inhibition of macromolecular synthesis was not sufficient to account for the 90% inhibition of infectious progeny formation. Encapsidation of polyoma DNA into mature virions appears to be completely inhibited after superinfection by beta-propiolactone-inactivated Sendai virus. Ultraviolet irradiation of live or beta-propiolactone-inactivated Sendai virus preparations abolishes the interfering capacity, indicating that a functional Sendai virus ribonucleic acid molecule is the interfering component.

Transient inhibition of polyoma virus synthesis by Sendai virus (parainfluenza I). I. Demonstration and nature of the inhibition by inactivated virus

Superinfection of polyoma virus-infected mouse embryo cells by beta-propiolactone-inactivated Sendai virus resulted in a 90% inhibition of the synthesis of infectious polyoma progeny. The interference is dependent upon the time of superinfection and the concentration of the inactivated virus. The inhibition of polyoma virus synthesis is transient in nature since normal synthesis of polyoma progeny virus is seen upon prolonged incubation. Interferon does not appear to be implicated in the interference. Various aspects of the biological and synthetic capabilities of beta-propiolactone-inactivated Sendai virus are also described.

Thymidine transport by cultured Novikoff hepatoma cells and uptake by simple diffusion and relationship to incorporation into deoxyribonucleic acid

The initial rate of thymidine-(3)H incorporation into the acid-soluble pool by cultured Novikoff rat hepatoma cells was investigated as a function of the thymidine concentration in the medium. Below, but not above 2 microM, thymidine incorporation followed normal Michaelis-Menten kinetics at 22 degrees , 27 degrees , 32 degrees , and 37 degrees C with an apparent K(m) of 0.5 microM, and the V(max) values increased with an average Q(10) of 1.8 with an increase in temperature. The intracellular acid-soluble (3)H was associated solely with thymine nucleotides (mainly deoxythymidine triphosphate [dTTP]). Between 2 and 200 microM, on the other hand, the initial rate of thymidine incorporation increased linearly with an increase in thymidine concentration in the medium and was about the same at all four temperatures. Pretreatment of the cells with 40 or 100 microMp-chloromercuribenzoate for 15 min or heat-shock (49.5 degrees C, 5 min) markedly reduced the saturable component of uptake without affecting the unsaturable component or the phosphorylation of thymidine. The effect of p-chloromercuribenzoate was readily reversed by incubating the cells in the presence of dithiothreitol. Persantin and uridine competitively inhibited thymidine incorporation into the acid-soluble pool without inhibiting thymidine phosphorylation. At concentrations below 2 microM, thymidine incorporation into DNA also followed normal Michaelis-Menten kinetics and was inhibited in an apparently competitive manner by Persantin and uridine. The apparent K(m) and K(i) values were about the same as those for thymidine incorporation into the nucleotide pool. The over-all results indicate that uptake is the rate-limiting step in the incorporation of thymidine into the nucleotide pool as well as into DNA. The cells possess an excess of thymidine kinase, and thymidine is phosphorylated as rapidly as it enters the cells and is thereby trapped. At low concentrations, thymidine is taken up mainly by a transport reaction, whereas at concentrations above 2 microM simple diffusion becomes the principal mode of uptake. Evidence is presented that indicates that uridine and thymidine are transported by different systems. Upon inhibition of DNA synthesis, net thymidine incorporation into the acid-soluble pool ceased rapidly. Results from pulse-chase experiments indicate that a rapid turnover of dTTP to thymidine may be involved in limiting the level of thymine nucleotides in the cell.